Supercritical transition mechanism of immiscible ethanol/hexadecane droplets

Although the properties of supercritical fluids have been significantly focused on, few studies have focused on the transition process of multicomponent fluids from the subcritical to supercritical state. Herein, the trans-critical behavior of an immiscible binary ethanol/hexadecane (EtOH/C-16) droplet under supercritical nitrogen environments is analyzed for the first time using molecular dynamics. The ambient pressure (p) and ambient temperature (T) of the droplets exceed the critical conditions for both EtOH and C-16. Moreover, trans-critical EtOH/C-16 droplets undergo a two-stage bulging-to-shrinking process. Liquid fraction lambda is introduced to quantify the structural characteristics of trans-critical fluids. Fluids inside the droplet are shown to transform from the vapor to liquid phase, signified by the increase in lambda with p. Three droplet evolution types are classified based on p: micro-explosion, puffing, and mixing types. The occurrence of each trans-critical droplet evolution type is determined by the competition between the subcritical gasification of EtOH and the supercritical pseudo-boiling of C-16. The supercritical transition of C-16 can be detected under each condition, while that of EtOH only occurs for the mixing-type droplet evolution. Furthermore, a p-T diagram is provided to analyze the combined effect of T and p on the trans-critical droplet evolution types. Published under an exclusive license by AIP Publishing.

Automated summary

In this study, molecular dynamics simulations were used to analyze the thermodynamic behavior of binary ethanol/hexadecane droplets under supercritical nitrogen environments. The droplets undergo a bulging-to-shrinking process during the transition from subcritical to supercritical state, and the fluids inside the droplets transform from vapor phase to liquid phase. The evolution types of the droplets were classified into micro-explosion, puffing, and mixing types based on the pressure condition.